Wellhead wicker repair tool

ABSTRACT

A wicker repair tool lands on a casing hanger within a wellhead. The wicker repair tool engages cutters with the inner diameter of the wellhead and rotates to reform wickers in the wellhead. The wicker repair tool includes a tubular member having an upper end that couples to a tubing string. A tubular tool head is formed on a lower end of the tubular member. At least one cutter is coupled to the tool head and is radially moveable between an engaged and a disengaged position. The cutters are adapted to engage an inner diameter surface of a wellhead so that rotation of the tool head relative to the wellhead will reform the wickers.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates in general to wellhead repairs and, in particular, to an apparatus and method for repairing wickers at a wellhead.

2. Brief Description of Related Art

Wellhead housings include wickers formed in the inner diameter surface of the wellhead housing prior to running the wellhead housing into the wellbore. Wickers comprise an annular inner diameter profile configured to engage devices and seals within the well and prevent axial movement of the engaged subsea devices and seals. Generally, wickers are small parallel, circumferential grooves. The grooves may deform an engaged surface, such as the surface of a casing hanger or a metal seal, radially in contact with the wickers. Wickers are generally formed near wellhead device landings so that after landing a device in the wellhead, the device, often through use of a wellhead seal, may engage the wickers and axially maintain its position within the wellhead. Subsea devices and seals engage the wickers in several ways. For example, the device may expand radially into the wickers, causing the wickers to deform the exterior surface of the device. Alternatively, the device may be pressed into an interference fit between another landed device and the wickers. Additional detail regarding wickers may be found in U.S. Pat. Nos. 4,960,172, 4,714,111, 4,561,499, and 5,255,746.

During drilling operations, tools and devices may drag across the wickers. The impact of these tools and devices on the wickers as they are dragged across the wickers causes the wickers to deform. As a consequence, at deformed locations, the wickers are no longer able to engage the device surface when the device is pressed into contact with the wicker. This results in a failure of the seal because fluid may flow past the seal at the location of the deformation of the wickers. For example, when setting a casing hanger, the hanger lands on a shoulder within the wellhead housing proximate to the wickers. A metal seal is then pressed into the gap between the hanger and the wellhead to seal and set the hanger by engaging the wickers. This seal prevents fluid flow through the annulus between the hanger and the wellhead housing and forms as a result of the engagement of the metal wickers to the metal surface of the seal. Damage to the wickers prevents seal engagement. Because the seal used to set the casing hanger cannot be engaged by the wickers at the damaged wicker location, the seal between the outer diameter of the casing hanger and the inner diameter of the wellhead necessary to set the casing hanger cannot be formed. Fluid will be able to flow through the annulus past the seal at the location of the wicker damage. Often, this may be overcome by use of an elastomeric ring run in place of, or in addition to, the metal seal. The elastomer ring will extrude into the damaged area of the wicker after landing. This “fixes” the damaged area of the wicker. A seal or subsea device can then be deformed into engagement with the wickers to create a fluid seal through the annulus with the elastomeric element completing the seal between the device and the wellhead.

Elastomeric sealing elements cannot “fix” damaged wickers in high pressure, high temperature, or low temperature situations. In such situations, the elastomer will significantly deviate from the needed elasticity, becoming too elastic or too inelastic. As a consequence, the elastomeric sealing element will be unable to deform into the damaged wicker areas or conversely flow at too great of a rate into the damaged wicker areas. Thus, the elastomer seals will fail to provide an effective solution to damaged wicker areas, potentially causing abandonment of the wellhead. In addition, use of elastomeric sealing elements significantly decreases the lifespan of the seal. Elastomeric sealing elements will wear faster than a metal seal even when not under the strain of a high pressure, high temperature, low temperature environment. Therefore, there is a need for an apparatus and method to repair damaged wickers on wellheads once the wellheads are positioned and secured within a wellbore without relying on elastomeric elements.

SUMMARY OF THE INVENTION

These and other problems are generally solved or circumvented, and technical advantages are generally achieved, by preferred embodiments of the present invention that provide an apparatus for repairing damaged wickers in wellheads, and a method for using the same.

In accordance with an embodiment of the present invention, an apparatus for repairing wickers in a bore of a wellhead member in place at an upper end of a wellbore is disclosed. The apparatus includes a tubular member having an upper end adapted to couple to a pipe string. An The apparatus also includes a tubular tool head coaxial with an axis of the tubular member. The tubular tool head is formed on a lower end of the tubular member for landing in the bore of the wellhead member. The apparatus further includes at least one cutter coupled to the tool head. The at least one cutter is radially moveable relative to the tool head between an engaged and a disengaged position. While in the engaged position, the at least one cutter is adapted to engage the wickers in the wellhead member so that rotation of the tool head relative to the wellhead member will re-cut and repair the wickers.

In accordance with another embodiment of the present invention, a subsea wellhead is disclosed. The subsea wellhead includes a subsea wellhead having a bore containing a set of wickers. A casing hanger is landed on a shoulder in the bore of the subsea wellhead adjacent the wickers. The subsea wellhead includes a wicker repair tool having an upper end that is threaded for coupling to a pipe string. The wicker repair tool is landed on an upper portion of the casing hanger so that a skirt portion of the wicker repair tool extends between the casing hanger and the subsea wellhead. The wicker repair tool includes at least one cutter coupled to the tool and radially moveable relative to the tool between a disengaged position outward to an engaged position. The cutter has a plurality of teeth that engage the wickers while in the engaged position so that rotation of the tool relative to the wellhead will re-cut the wickers.

In accordance with yet another embodiment of the present invention, a method for repairing wickers in a bore of a subsea wellhead is disclosed. The method begins by running a wicker repair tool on a pipe string and landing the tool on a casing hanger within the bore of the subsea wellhead. Next, the method actuates a cutter of the wicker repair tool to engage the wickers of the subsea wellhead. Then, the method rotates the wicker repair tool to re-cut the wickers in the subsea wellhead.

An advantage of a preferred embodiment is that the disclosed embodiments provide an apparatus and method to repair wickers in a wellhead after the wellhead is installed within a wellbore. The disclosed embodiments allow for use of a metal seal without the addition of elastomeric elements to complete the seal between the metal seal and the damaged wickers. In addition, by repairing the wellhead with the apparatus disclosed herein, wellhead abandonment is prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the features, advantages and objects of the invention, as well as others which will become apparent, are attained, and can be understood in more detail, more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof which are illustrated in the appended drawings that form a part of this specification. It is to be noted, however, that the drawings illustrate only a preferred embodiment of the invention and are therefore not to be considered limiting of its scope as the invention may admit to other equally effective embodiments.

FIG. 1A is a partial sectional schematic view of a wicker repair tool.

FIGS. 1B and 1C are a partial sectional schematics of a portion of the wicker repair tool of a FIG. 1A.

FIG. 2 is a sectional schematic view of the wicker repair tool of FIG. 1A, in place in a subsea wellhead.

FIG. 3 is a partial sectional schematic view of the wicker repair tool of FIG. 1A, in a disengaged position.

FIG. 4 is a partial sectional view of damaged wickers in a wellhead.

FIG. 5 is a partial sectional view of the wicker repair tool of FIG. 1A engaged with the damaged wickers of FIG. 4.

FIG. 6 is a partial sectional view of repaired wickers in a wellhead.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will now be described more fully hereinafter with reference to the accompanying drawings which illustrate embodiments of the invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout, and the prime notation, if used, indicates similar elements in alternative embodiments.

In the following discussion, numerous specific details are set forth to provide a thorough understanding of the present invention. However, it will be obvious to those skilled in the art that the present invention may be practiced without such specific details. Additionally, for the most part, details concerning wellhead assembly, completion, operation, use, and the like have been omitted inasmuch as such details are not considered necessary to obtain a complete understanding of the present invention, and are considered to be within the skills of persons skilled in the relevant art.

Referring to FIG. 1A, there is shown a wicker repair tool 11. Wicker repair tool 11 has an engaged position, shown in FIG. 1A, and a disengaged position, shown in FIG. 3. As shown in FIG. 1A, wicker repair tool 11 includes a tubular member 13 defining a central bore 15 for the passage of fluids. Bore 15 has an axis 17. A tool head 19 is formed on an end of tubular member 13 opposite a coupler 21. Coupler 21 is configured to couple wicker repair tool 11 to a tubing string (not shown). In the illustrated embodiment, tool head 19 has an exterior diameter 23 greater than the exterior diameter of tubular member 13. Tool head 19 tapers from exterior diameter 23 of tubular member 13 to exterior diameter 23 of tool head 19. Exterior diameter 23 may be a diameter slightly smaller than an inner diameter of a subsea wellhead (not shown in FIG. 1A) so that tool head 19 may insert into an inner diameter cavity of a subsea wellhead as illustrated and described below with respect to FIG. 2.

Still referring to FIG. 1A, wicker repair tool 11 includes a cutter actuation assembly formed in tool head 19 and tubular member 13. As a portion of the cutter actuation assembly, tool head 19 may define a piston cavity 25. In the exemplary embodiment, piston cavity 25 comprises a cavity having a diameter approximately equal to the diameter of bore 15. A piston 27 may insert into piston cavity 25, substantially filling a width of piston cavity 25. As illustrated, piston 27 may seal within piston cavity 25 so that fluid in bore 15 may not pass to an area of piston cavity 25 axially below piston 27. A person skilled in the art will understand that any suitable sealing mechanism may be used. Tool head 19 includes a spring 29 within piston cavity 25 axially beneath piston 27. In the illustrated embodiment, a lower end of spring 29 rests on a seat (not shown) proximate to a bottom of piston cavity 25, and a lower end of piston 27 rests on an upper end of spring 29 so that if piston 27 moves axially downward spring 29 will exert a reactive force axially upward in response. As illustrated in FIG. 1A, spring 29 is compressed by piston 27.

Tool head 19 includes a plurality of hydraulic ports 31. In the exemplary embodiment, hydraulic ports 31 extend from an exterior of tool head 19 on the tapered surface of tool head 19 into upper hydraulic passages 33 formed in tool head 19. External hydraulic lines 32 (FIG. 2) may be coupled to hydraulic ports 31 to supply hydraulic pressure into upper hydraulic passages 33 during operation of wicker repair tool 11. Hydraulic lines 32 may also be use to test the operation of wicker repair tool 11 while wicker repair tool is still on the surface. Alternatively, hydraulic fluid may be supplied through hydraulic ports 31 to upper hydraulic passages 33, and piston cavity 25, lower hydraulic passages 43 (described in more detail below) prior to run-in of wicker repair tool 11. After filling lower hydraulic passages 43, piston cavity 25, and upper hydraulic passages 33, hydraulic ports 31 may be plugged sealing upper and lower hydraulic passages 33, 43, and piston cavity 25. Wicker repair tool 11 may then be run to the wellhead without hydraulic lines 32. Upper hydraulic passages 33 extend between hydraulic ports 31 and piston cavity 25, terminating below piston 27 while piston 27 is in its upper position to supply fluid pressure from an external source to piston cavity 25. Hydraulic fluid may pass through a center of spring 29 as described in more detail below.

Tool head 19 includes a cylindrical cutter extension or skirt 35 protruding from a lower portion of tool head 19. Cutter extension 35 comprises an annular protrusion having an exterior diameter equal to exterior diameter 23 of tool head 19, and an inner diameter defining a subsea member cavity 37. Subsea member cavity 37 is of a size and shape to accommodate a subsea tubular member, such as a tubing hanger, disposed in a subsea wellhead, as described in more detail below with respect to FIG. 2.

Continuing to refer to FIG. 1A, a plurality of cutters 39 are secured to cutter extension 35. Each cutter 39 has a radially exterior surface having a plurality of teeth. The teeth of each cutter 39 are adapted to match the shape and pitch of the wickers to be repaired. The teeth of each cutter 39 have a sufficient hardness, strength, etc., to engage and cut or deform the material of which the wickers are formed. Cutters 39 couple to cutter extension 35 so that they may move between an engaged position shown in FIG. 1A, and a disengaged position shown in FIG. 3. As shown in FIG. 1A, cutters 39 are actuated radially outward by a plurality of cutter actuators 41 with a separate cutter actuator 41 proximate to each respective cutter 39. In the illustrated embodiment, four cutters 39 and four cutter actuators 41 are used. A person skilled in the art will understand that more or fewer cutters 39 and cutter actuators 41 may be used. Cutter actuators 41 reside within lower hydraulic passages 43 formed in a lower portion of tool head 19. A lower hydraulic passage 43 extends between a lower end of piston cavity 25, axially beneath spring 29 to each cutter actuator 41 proximate to cutters 39. Cutter actuators 41 substantially fill the diameter of the proximate lower hydraulic passage 43 and are sealed to lower hydraulic passages 43 by any suitable means such as with the illustrated o-rings. Buildup of hydraulic pressure within hydraulic passage 43 will exert a force on an upper end of cutter actuators 41, causing cutter actuators 41 to move downward to the engaged position shown in FIG. 1A. Lower hydraulic passages 43 are in fluid communication with piston cavity 25 such that fluid passing from upper hydraulic passages 33 into piston cavity 25 may then flow into lower hydraulic passages 43.

Cutter actuators 41 have a tapered lower end adapted to interface with a tapered interior surface of cutters 39. When fluid pressure builds up within hydraulic passage 43, the fluid pressure will cause cutter actuator 41 to move axially downward in response such that the lower end of each cutter actuator 41 will slide across the interior surface of a respective cutter 39, moving the adjacent cutter 39 radially outward in response. In the illustrated embodiment, the interface between cutter actuator 41 and cutter 39 comprises a pair of facing ramped surfaces.

Cutters 39 are biased to the disengaged position as described with respect to FIGS. 1B and 1C. As shown in FIG. 1B, each cutter 39 includes a retaining lug 63. Retaining lug 63 extends from a lower portion of each cutter 39 into a recess 65 formed axially below each cutter 39. Recess 65 extends from the outer diameter surface of cutter extension 35 radially inward to a radially outward facing shoulder 67. Recess 65 has a radial depth substantially equal to the depth of each cutter 39 such that when a radially inward surface of retaining lug 63 abuts shoulder 67, teeth 62 do not protrude beyond the radially outward surface of cutter extension 35. Recess 65 includes a retaining recess 68 on an axially downward portion of recess 65. Retaining recess 68 extends from the radially outward surface of cutter extension 35 to a radially outward facing shoulder 69. A retaining plate 71 is secured to cutter extension 35 within retaining recess 68 at shoulder 69. An exterior surface of retaining plate 71 is substantially flush with the exterior surface of cutter extension 35 and abuts shoulder 69 and a lower end of cutter 39 such that cutter 39 may slide across an upper end rim of retaining plate 71. A spring member, such as a wave spring 73, is interposed between retaining lug 63 and retaining plate 71. In the illustrated embodiment, radial displacement of wave spring 73 will exert a radially inward force on retaining lug 63.

As shown in FIG. 1C, when cutter actuator 41 moves radially downward to engage cutter 39 with wickers 58 of wellhead 57, wave spring 73 will be compressed between retaining lug 63 and retaining plate 71. When piston 27 moves axially upward following repair of wickers 58, the compressed wave spring 73 will exert a radially inward force on retaining lug 63. In response, cutter 39 will move radially inward, causing the interior surface of cutter 39 to slide past the lower end of cutter actuator 41, moving cutter actuator 41 axially upward into lower hydraulic passages 43.

A centralizing plate 45 couples to a lower end of tool head 19 at a terminus of subsea member cavity 37 through a bearing 49. Centralizing plate 45 has an outer diameter such that when centralizing plate 45 lands on a subsea member as described in more detail below, the outer diameter of centralizing plate 45 will approximately coincide with the outer diameter of the subsea member. Centralizing plate 45 may frictionally engage a rim of a subsea member as described in more detail below with respect to FIG. 2. As shown in FIG. 1A, a plate protrusion 47 extends from a lower portion of centralizing plate 45 and has a base outer diameter where plate protrusion 47 joins centralizing plate 45. The base outer diameter of plate protrusion 47 is approximately equal to an inner diameter of a subsea member, such that when tool head 19 lands on a subsea member, plate protrusion 47 will substantially fill the inner diameter of the subsea member, as described in more detail below. Plate protrusion 47 tapers from the base outer diameter at centralizing plate 45 to a narrower diameter at its outer terminus. A portion of centralizing plate 45 extends in a horizontal manner from the base of plate protrusion 47 to the outer diameter of centralizing plate 45.

Bearing 49 may be interposed between tool head 19 and centralizing plate 45. Bearing 49 resides within a bearing recess 51 such that centralizing plate 45 may couple to bearing 49. Bearing 49 in turn couples to tool head 19. Bearing 49 supports the axial load of centralizing plate 45, and allows centralizing plate 45 to rotate within cavity 37 relative to tool head 19 and tool head 19 to rotate relative to centralizing plate 45. Bearing 49 may be any suitable bearing type, such as sealed roller bearings.

During a drilling operation, a casing hanger 55 will run down a drilling riser and land in the position shown in FIG. 2 within a wellhead 57. Wellhead 57 is shown schematically and may be a variety of types, including varieties of both surface and subsea wellheads. Operators will then attempt to set casing hanger 55 with a wellhead seal in a conventional manner similar to that described in U.S. Pat. No. 4,960,172. Following setting of the wellhead seal, an attempt will be made to test the seal to ensure proper setting of casing hanger 55. If the test of the wellhead seal at casing hanger 55 fails, the seal will be pulled, and wicker repair tool 11 will be used as described below to repair wickers at casing hanger 55 so that casing hanger 55 may be set to wellhead 57.

Referring to FIG. 6, wickers 58 are small, parallel, circumferential grooves. Each wicker 58 is triangular in cross-section with upper and lower flanks that incline the same amount relative to the longitudinal axis of wellhead 57. Wickers 58 have a constant depth. Preferably, the depth is about one-eight of an inch. Referring to FIG. 4, after other drilling operations, wickers 58 may have a damaged profile 60 at multiple locations. Attempts to set a metal seal to the damaged profile 60 of wickers 58 as described above will result in seal failure.

In operation, wicker repair tool 11 couples to tubing string 53 and is run to the position shown in FIG. 2. As illustrated in FIG. 2, wicker repair tool 11 lands on a casing hanger 55. Cutter extension 35 will land between an outer diameter of casing hanger 55 and an inner diameter of subsea wellhead 57. Plate protrusion 47 will land within an inner diameter cavity 59 of casing hanger 55. The tapered surface of plate protrusion 47 will guide the exterior end of plate protrusion 47 into engagement with and align centralizing plate 45 coaxially with casing hanger 55. As a result, wicker repair tool 11 will align with and be coaxial with casing hanger 55. In the exemplary embodiment, a lower surface of centralizing plate 45 extending between the outer diameter of centralizing plate 45 and the outer base diameter of plate protrusion 47 will abut a rim 61 of casing hanger 55, frictionally engaging casing hanger 55.

When landing on casing hanger 55, the components of tool head 19 will be in the positions shown in FIG. 3. Cutters 39 will be in the retracted, disengaged position, and cutter actuators 41 will reside in upper positions within lower hydraulic passageways 43. Piston 27 will be at an elevated position within piston cavity 25, and spring 29 will be at rest as shown in FIG. 3. After landing on casing hanger 55, as shown in FIG. 2, fluid pressure will be supplied through external hydraulic lines 32 and hydraulic ports 31 to substantially fill upper and lower hydraulic passages 33, 43, and piston cavity 25. Alternatively, fluid pressure may be supplied to upper and lower hydraulic passages 33, 43, and piston cavity 25 and hydraulic ports 31 plugged prior to run-in of wicker repair tool 11. In the alternative case, hydraulic lines 32 will not extend downhole to wicker repair tool 11 during operation.

In both embodiments, fluid will then be circulated down central bore 15 until the fluid pressure uphole from piston 27 exerts an axially downward force on piston 27. In response, piston 27 moves axially downward, compressing spring 29 and forcing fluid in piston cavity 25 axially beneath piston 27 into lower hydraulic passageways 43. In response, cutter actuators 41 move axially downward from their position in FIG. 3. The lower end of each cutter actuator 41 will come into contact with and slide past the interior surface of a respective cutter 39, moving the corresponding cutter 39 from the disengaged position illustrated in FIG. 3 to the engaged position illustrated in FIG. 1A. As shown in FIG. 5, cutters 39 will engage the inner diameter surface of wellhead 57. A person skilled in the art will understand that cutters 39 and cutter actuators 41 may be adapted so that cutters 39 will engage the outer diameter of casing hanger 55 to reform wickers of casing hanger 55.

As shown in FIG. 5, movement of cutters 39 from the disengaged position to the engaged position will bring an exterior surface of each cutter 39 into contact with damaged profile 60 of wickers 58 of wellhead 57. The exterior surface of each cutter 39 includes a plurality of teeth or cutting elements 62 having a sufficient hardness, strength, etc., to engage the material of wellhead 57 at wickers 58 and deform damaged profile 60 into wickers 58 as shown in FIG. 6. The set of teeth 62 preferably has an axial length the same as the axial length of wickers 58 so that all of wickers 58 are engaged at the same time.

Once cutters 39 engage the inner diameter surface of wellhead 57, as shown in FIG. 5, wicker repair tool 11 will be rotated by tubing string 53. As described above, wicker repair tool 11 will rotate relative to casing hanger 55 and wellhead 57 on centralizing plate 45 and bearing 49. Rotation of wicker repair tool 11 causes cutters 39 to cut wickers into the inner diameter surface of wellhead 57. In an exemplary embodiment, when landing on casing hanger 55, cutters 39 will align with previously formed wickers in wellhead 57. Thus, when cutters 39 engage wellhead 57 and rotate to cut wickers, cutters 39 will reform existing wickers in wellhead 57, as shown in FIG. 6, repairing damage done during previous running operations. During rotation of wicker repair tool 11, fluid pressure will be maintained on piston 27 and through hydraulic ports 31 to maintain engagement of cutters 39 to the inner diameter of wellhead 57.

As shown in FIG. 2, after landing and engagement of cutters 39, wicker repair tool 11 is rotated through a sufficient number of revolutions to ensure that wickers have been reformed/re-cut in wellhead 57 to repair damaged profile 60 of FIG. 4 to the profile of wickers 58 in FIG. 6. Rotation of wicker repair tool 11 then stops, and fluid pressure is removed from the upper surface of piston 27; in response, spring 29 exerts an axial spring force on a lower surface of piston 27. This causes piston 27 to move upward axially and relieve fluid pressure from piston cavity 25 and lower hydraulic passages 43. In response, cutters 39, biased to the disengaged position, will move from the engaged position of FIG. 1A to the disengaged position of FIG. 3, moving cutter actuators 41 to their positions within lower hydraulic passages 43 as shown in FIG. 3. Wicker repair tool 11 may then be pulled from the wellbore and casing hanger 55 may be set in a normal operation.

Accordingly, the disclosed embodiments provide numerous advantages. For example, the disclosed embodiments provide a means to repair wickers in a damaged wellhead. By re-cutting the wickers on an interior diameter surface, devices are again able to seal and set within the wellhead. This prevents abandonment of the wellhead. In addition, use of the disclosed embodiments allows for sealing and setting of devices within the wellhead without the need for additional elastomer seals; this can reduce the number of trips needed to land, set, and run a device. Removing the need of elastomer seals is especially useful in high pressure and temperature situations where elastomer seals cannot repair damaged wicker areas due to the change in elastic properties of the seal caused by the environment. Thus, the disclosed embodiments provide a means to repair damaged wickers and continue use of metal wellhead seals. Wickers in a tubing head for tubing hanger seals could be repaired in a similar manner. Wickers on the exterior of casing and tubing hangers could be repaired similarly.

It is understood that the present invention may take many forms and embodiments. Accordingly, several variations may be made in the foregoing without departing from the spirit or scope of the invention. Having thus described the present invention by reference to certain of its preferred embodiments, it is noted that the embodiments disclosed are illustrative rather than limiting in nature and that a wide range of variations, modifications, changes, and substitutions are contemplated in the foregoing disclosure and, in some instances, some features of the present invention may be employed without a corresponding use of the other features. Many such variations and modifications may be considered obvious and desirable by those skilled in the art based upon a review of the foregoing description of preferred embodiments. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention. 

1. An apparatus for repairing wickers in a bore of a wellhead member in place at an upper end of a wellbore, the apparatus comprising: a tubular member having an upper end adapted to couple to a pipe string, the tubular member having an axis; a tubular tool head coaxial with and formed on a lower end of the tubular member for landing in the bore of the wellhead member; at least one cutter coupled to the tool head, the at least one cutter radially moveable relative to the tool head between an engaged and a disengaged position; and while in the engaged position, the at least one cutter adapted to engage the wickers in the wellhead member so that rotation of the tool head relative to the wellhead member will re-cut and repair the wickers.
 2. The apparatus of claim 1, wherein the tool head comprises: a cylindrical extension extending from a lower portion of the tool head, the cylindrical extension defining an interior cavity for reception over a hanger located in the wellhead member; the at least one cutter being carried on an exterior diameter portion of the cylindrical extension; and a cutter actuation assembly secured to the tool head to selectively move the cutters between the engaged and disengaged positions.
 3. The apparatus of claim 2, the tool head further comprising: a centralizing plate having an exterior diameter less than the inner diameter of the cavity; and the centralizing plate rotatably coupled to a lower portion of the tool head within the cavity so that the centralizing plate of the tool head lands on the hanger within the wellhead and locates the tool head coaxial with the hanger.
 4. The apparatus of claim 3, wherein a bearing is interposed between the centralizing plate and the tool head so that the tool head may rotate relative to the centralizing plate.
 5. The apparatus of claim 1, wherein the cutter actuation assembly comprises: a piston cavity defined by the tool head in an interior of the tool head axially beneath the tubular member; a piston positioned coaxial with the tubular member within the piston cavity so that the piston moves in response to fluid pressure applied to the pipe string to move the cutter to the engaged position; and at least one cutter actuator retained by the tool head proximate to the at least one cutter, the at least one cutter actuator engaging the at least one cutter and moving the cutter in response to fluid pressure applied by movement of the piston.
 6. The apparatus of claim 5, wherein: the at least one cutter actuator has a ramped surface facing the at least one cutter; and the at least one cutter has a ramped surface facing the at least one cutter actuator so that when the at least one cutter actuator moves axially relative to the at least one cutter, the ramped surface of the at least one cutter actuator will slidingly abut the ramped surface of the at least one cutter, moving the at least one cutter radially in response.
 7. The apparatus of claim 6, wherein the cutter is biased to the disengaged position.
 8. The apparatus of claim 5, further comprising: a spring coaxial with the piston and positioned to bias the piston axially upward; and hydraulic lines extending between hydraulic ports on an upper portion of the tool head and the piston and further extending between the piston and the cutters, an end of the at least one cutter actuator residing within the hydraulic lines.
 9. The apparatus of claim 1, further comprising: a hydraulically powered actuator carried in the tool head in engagement with the cutter for moving the cutter from the disengaged to the engaged position; and a biasing spring carried in the tool head in engagement with the cutter for moving the cutter from the engaged to the disengaged position.
 10. A subsea wellhead comprising: a subsea wellhead having a bore containing a set of wickers; a casing hanger landed on a shoulder in the bore of the subsea wellhead adjacent the wickers; a wicker repair tool having an upper end that is threaded for coupling to a pipe string; the wicker repair tool landing on an upper portion of the casing hanger so that a skirt portion of the wicker repair tool extends between the casing hanger and the subsea wellhead; the wicker repair tool comprising: at least one cutter coupled to the wicker repair tool and radially moveable relative to the wicker repair tool between a disengaged position outward to an engaged position; and the cutter having a plurality of teeth that engage the wickers while in the engaged position so that rotation of the wicker repair tool relative to the wellhead will re-cut the wickers.
 11. The system of claim 10, the wicker repair tool further comprising: a centralizing plate located within the skirt portion and landing on the hanger; and the wicker repair tool centralizing plate being rotatable relative to a tool head of the wicker repair tool.
 12. The system of claim 11, wherein a bearing is interposed between the centralizing plate and the tool head.
 13. The system of claim 10, wherein the wicker repair tool further comprises a cutter actuation assembly to actuate the cutters between the engaged and disengaged positions in response to fluid pressure applied down the pipe string.
 14. The system of 13, wherein the cutter actuation assembly comprises: a piston cavity adapted to be in fluid communication with the pipe string; at least one cutter actuator retained by the tool head proximate to the at least one cutter, the at least one cutter actuator being axially moveable in response to movement of the piston and engaging the at least one cutter; and a piston positioned within the piston cavity so that the piston moves downward in response to fluid pressure supplied from the pipe string.
 15. The system of claim 14, wherein the cutter actuation assembly further comprises: the at least one cutter actuator having a ramped surface facing the at least one cutter; and the at least one cutter having a ramped surface facing the at least one cutter actuator so that when the at least one cutter actuator moves axially relative to the at least one cutter, the ramped surface of the at least one cutter actuator will slidingly abut the ramped surface of the at least one cutter, moving the at least one cutter radially in response.
 16. The system of claim 15, wherein the cutter actuation assembly further comprises: a spring coaxial with the piston and positioned so that the spring may resist axial motion of the piston; and hydraulic lines extending between hydraulic ports on an upper portion of the tool head and the piston and further extending between the piston and the cutters, an end of the at least one cutter actuator residing within the hydraulic lines.
 17. A method for repairing wickers in a bore of a subsea wellhead, the method comprising: (a) running a wicker repair tool on a pipe string and landing the wicker repair tool on a casing hanger within the bore of the subsea wellhead; (b) actuating a cutter of the wicker repair tool to engage the wickers of the subsea wellhead; then (c) rotating the wicker repair tool to re-cut the wickers in the subsea wellhead.
 18. The method of claim 17, wherein step (b) comprises applying fluid pressure down the pipe string.
 19. The method of claim 17, wherein step (b) comprises dispensing a hydraulic fluid down a hydraulic line extending from a drilling rig to the wicker repair tool.
 20. The method of claim 17, wherein step (c) comprises rotating the pipe string. 